The United States military aero engine designation system was introduced in 1926, originally for piston engines it was expanded in the 1947 to include a separate system for turbine and rocket engines.

Piston engines

A piston engine designation has three separate elements, a type prefix, a number representating engine displacement and a model number.

Type Prefix

The type prefix is based on the engine disposition:

H	Two-row inline Aircraft engine An aircraft engine is the component of the propulsion system for an aircraft that generates mechanical power. Aircraft engines are almost always either lightweight piston engines or gas turbines...
L	Inline Aircraft engine An aircraft engine is the component of the propulsion system for an aircraft that generates mechanical power. Aircraft engines are almost always either lightweight piston engines or gas turbines...
O	Opposed Aircraft engine An aircraft engine is the component of the propulsion system for an aircraft that generates mechanical power. Aircraft engines are almost always either lightweight piston engines or gas turbines...
R	Radial Radial engine The radial engine is a reciprocating type internal combustion engine configuration in which the cylinders point outward from a central crankshaft like the spokes on a wheel...
V	Vee Aircraft engine An aircraft engine is the component of the propulsion system for an aircraft that generates mechanical power. Aircraft engines are almost always either lightweight piston engines or gas turbines...
W	W engine W engine A W engine is a type of reciprocating engine arranged with its cylinders in a configuration in which the cylinder banks resemble the letter W, in the same way those of a V engine resemble the letter V....
X	X engine X engine An X engine is a piston engine comprising twinned V-block engines horizontally opposed to each other. Thus, the cylinders are arranged in four banks, driving a common crankshaft. Viewed head-on, this would appear as an X...

Some early engines had the type letter prefixed by a modification letter

• G - geared
• I - inverted
• S - supercharged

Displacement

A number related to the engine displacement within 5 cubic inches.

Model Suffix
Letters were used between 1926 and 1933 then suffixes were numerals with odd number for Army and later Air Force engines and even numbers for Navy engines. After 1943 the letters AN were included to indicate the engine met both Army/Air Force and Navy requirements. Some engines fitted with water-injected engines had the W added to the suffix.

For example the Curtiss V-1150-1 is a Vee-type engine with a displacement of 1150 cubic inches and is an Army model.

Turbine engines

A turbine engine designation consists of four separate elements in the format TSS-MM-NN where T is the type letter, SS is the sequence number, MM is the manufacturer designation (one or two characters), and NN is the model number:

Type letter

J	Jet engine Jet engine A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...
T	Turboprop Turboprop A turboprop engine is a type of turbine engine which drives an aircraft propeller using a reduction gear.The gas turbine is designed specifically for this application, with almost all of its output being used to drive the propeller...
TF or F	Turbofan Turbofan The turbofan is a type of airbreathing jet engine that is widely used for aircraft propulsion. A turbofan combines two types of engines, the turbo portion which is a conventional gas turbine engine, and the fan, a propeller-like ducted fan...

The prefixes X for experimental and Y for service test are used.

Sequence number

Each type has its own sequence which started at 30.

Manufacturer designation

A	Allison Engine Company Allison Engine Company The Allison Engine Company was a U.S. aircraft engine manufacturer. In 1929, shortly after the death of James Allison, the company was purchased by the Fisher brothers. Fisher sold the company to General Motors, who owned it for most of its history...
AC	Allis-Chalmers
AJ	Aerojet Aerojet Aerojet is an American rocket and missile propulsion manufacturer based primarily in Rancho Cordova, California with divisions in Redmond, Washington, Orange, Gainesville and Camden, Arkansas. Aerojet is owned by GenCorp. They are the only US propulsion company that provides both solid rocket...
B	Buick Buick Buick is a premium brand of General Motors . Buick models are sold in the United States, Canada, Mexico, China, Taiwan, and Israel, with China being its largest market. Buick holds the distinction as the oldest active American make...
BO	Boeing Boeing The Boeing Company is an American multinational aerospace and defense corporation, founded in 1916 by William E. Boeing in Seattle, Washington. Boeing has expanded over the years, merging with McDonnell Douglas in 1997. Boeing Corporate headquarters has been in Chicago, Illinois since 2001...
CW	Curtiss-Wright Curtiss-Wright The Curtiss-Wright Corporation was the largest aircraft manufacturer in the United States at the end of World War II, but has evolved to largely become a component manufacturer, specializing in actuators, aircraft controls, valves, and metalworking....
F	Ford
FF	Frederic Flader
G	Garrett AiResearch Garrett AiResearch Garrett AiResearch was a manufacturer of turboprop engines and turbochargers, and a pioneer in numerous aerospace technologies. It was previously known as Aircraft Tool and Supply Company, Garrett Supply Company, AiResearch Manufacturing Company, or simply AiResearch...
GE	General Electric
GN	Giannini
K	Kellog
L	Lycoming Lycoming Engines Lycoming Engines is a U.S. aircraft engine company, known primarily for its general aviation engines. For most of its history Lycoming has been part of the AVCO group as AVCO Lycoming. In 1987 AVCO was purchased by Textron to become Textron Lycoming...
LA	Lockheed
LD	Avco Lycoming Lycoming Engines Lycoming Engines is a U.S. aircraft engine company, known primarily for its general aviation engines. For most of its history Lycoming has been part of the AVCO group as AVCO Lycoming. In 1987 AVCO was purchased by Textron to become Textron Lycoming...
MA	Marquardt
MN	Mensasco
NH	Northrop-Hendy
OEL	Orenda
P	Pratt & Whitney Pratt & Whitney Pratt & Whitney is a U.S.-based aerospace manufacturer with global service operations. It is a subsidiary of United Technologies Corporation . Pratt & Whitney's aircraft engines are widely used in both civil aviation and military aviation. Its headquarters are in East Hartford, Connecticut, USA...  / United Aircraft of Canada
R	Fairchild
RM	Reaction Motors Reaction Motors Reaction Motors Inc. was an early American maker of liquid-fueled rocket engines, located in New Jersey. RMI engines with thrust powered the Bell X-1 rocket aircraft that first broke the sound barrier in 1947, and later successors including the X-1A, X1E, and the D558-2 Douglas Skyrocket...
T	Continental
V	Packard Packard Packard was an American luxury-type automobile marque built by the Packard Motor Car Company of Detroit, Michigan, and later by the Studebaker-Packard Corporation of South Bend, Indiana...
W	Wright
WE	Westinghouse

Model number

Odd numbers for the United States Air Force and even numbers for the United States Navy

For example the J79-GE-10 is a Turbojet built by General Electric and is a Navy model.

Rocket engines

Have a similar system to turbine engines but use three basic types:

LR	Liquid-fuel
PS	Pulsejet
RJ	Ramjet Ramjet A ramjet, sometimes referred to as a stovepipe jet, or an athodyd, is a form of airbreathing jet engine using the engine's forward motion to compress incoming air, without a rotary compressor. Ramjets cannot produce thrust at zero airspeed and thus cannot move an aircraft from a standstill...

The prefixes X for experimental and Y for service test are used.